The present invention relates in general to numerical control manufacture and more specifically to a system and method to compensate for vertical deflection during manufacture.
Some manufacturing processes, for example fiber placement, require exact definition of part location to be successful. The placement and orientation of individual fibers of a fiber part must be consistent and within the allowable limits of spacing between fibers or courses of fibers. Hand-lay up of fiber parts is typically performed for large or unusually shaped objects. When larger parts are required, and the number of individual fibers or fiber sheets increases because of the size of the part, the amount of time required to lay-up the fiber parts becomes prohibitive.
Manufacturing processes using numerically controlled (NC) machines have been used to manufacture fiber components. With the NC machines commonly used, improvements in speed and quality are achieved in smaller parts. When an NC machine is used, a mold or tool is placed on the machine about which the fibers are laid, before the fibers are heat treated to harden the part. The tool can be supported from one end (i.e., cantilevered) or supported from both ends. The tool will normally deflect both due to gravity along its unsupported length and based on its cross sectional shape. NC machines normally provide one or more supports to minimize sag from gravity deflection. It is undesirable, however, to support a fiber laminating tool at any location where the laminate is applied because the support must contact the tool, interfering with the laying of individual fibers on the part. Tool deflection during the lamination process therefore results in laminate being incorrectly applied.
Methods to identify and compensate for the amount of gravity induced deflection of the tool are known. In one method, a maximum deflection of the tool is calculated and the average deflection is used as an incremental change for the NC tool applying the individual laminate fibers. The use of an average deflection can over-compensate some areas of the component and under-compensate other areas of the component. By not properly compensating the amount of sag for the position the laminate application head of the NC machine is at, the fibers can be misplaced or spaced inappropriately causing part defects. In highly stressed components such as used in the commercial aircraft industry, fiber laminated components are used. Defective parts having fibers laminated with improper spacing or at an improper angle do not produce acceptable parts for high stress applications.
It is therefore desirable to provide a method and a system to compensate for the gravity-induced deflection of the tools used for laminate construction of laminated parts.
According to a preferred embodiment of the present invention, a method and system are provided to compensate for vertical deflection of the tools used for laminate manufacture. A numerical manufacturing model to manufacture a part is developed based on its nominal (i.e., non-deflected) dimensions and is loaded in a computer database as a plurality of motion statements. A set of material properties for the part including the number of laminate layers and laminate layer directions are also programmed into the computer. The part is typically laminated over a tool (acting as a mold) that is supported on at least one end, and a vertical deflection of the tool due to gravity results. The vertical deflection of the tool, hereinafter referred to as sag, is calculated or measured. A dimensional difference between the calculated or measured tool sag and the numerical manufacturing model is calculated. The calculated dimensional difference is applied as a compensation value during part manufacture to ensure the part dimensionally matches the numerical manufacturing model.
Because a variety of part shapes are manufactured using an NC machine, a variety of individual tools to support those shapes are also used. Each individual tool can sag differently over an unsupported length of the tool. The amount of sag is determined by calculation, or by measuring the actual tool, and a set of actual sag values is produced. A representative quantity of the actual sag values are input into a computer database in a lookup table. For each given motion statement, (i.e., for each nominal position along the part being manufactured) the computer interpolates between the representative values in the lookup table to produce a sag value for that nominal location. The sag value is applied to the given motion statement to direct the vertical position of a laminate application head of the NC machine. The laminate application head is thereby positioned to a tool actual location, allowing for tool sag, for each part nominal coordinate.
The lookup table provides the representative sag values based on C-axis rotation position and Z-axis position (i.e., horizontal position) on the tool. The number of representative sag values in the lookup table is controlled at the user""s discretion based on the geometry and length of the part being manufactured. A macro interrogates each motion statement for part coordinate values. The lookup table is entered using the part coordinate values and a sag value is calculated by interpolating between the Z-axis positions and the C-axis rotation positions closest to the part coordinate values. A Z-Index value is input by the user. The Z-Index value can be applied to each calculated sag value to index the lookup table values to a global tool horizontal position on the NC machine. A multiplier is also input by the user. The multiplier can be used to adjust up or down the calculated sag value generated by data derived from the lookup table. The above process is repeated for each subsequent motion statement until the end of the file is reached.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.